The present invention relates to the testing of analog and mixed-signal circuits. More particularly, although not exclusively, the present application relates to the testing of analog and/or mixed-signal circuits using Dynamic Element Matching for effective source linearization or effective precision waveform generation.
The use of mixed-signal circuits continues to grow. At the same time, the performance capabilities of these circuits are also increasing. This creates significant problems in testing. For example, when producing components having high performance, even the best commercial test equipment only has performance capabilities that are marginally capable of testing such state of the art parts. In addition, there are emerging integrated circuits that have performance capabilities that will exceed that of the best available commercial testers. Therefore, the use of commercial production testers can be problematic.
An alterative to using commercial production testers is to do testing in a built-in-self-test (BIST) environment. Self-testing or partial self-testing can reduce or eliminate production testing costs. However, in many cases the use of BIST is simply not practical because the testing circuitry may have greater complexity and/or area requirements than the device under test.
Most prior art analog and mixed-signal testing requires very precise excitations which are costly to generate whether they be in a production environment or a BIST environment. The time required to generate precision excitations in a production test environment may also be exceedingly long because, in part, of settling concerns but long settling time is in direct conflict with source stationarity concerns. The cost of production testing of some analog and mixed-signal circuits has become very high because of the expense associated with the production testers and because of the time many circuits require on these testers. In a BIST environment, the requirements for the excitations are so severe that there is little industrial adoption of existing techniques for mixed-signal functions.
Although seemingly unrelated to testing, at least to one not having the benefit of this disclosure, dynamic element matching (DEM) techniques have been around for some time in circuit design (as opposed to testing) of components such as data converters. DEM recognizes that element matching errors are inevitable due to inherent process variations. Although special layout techniques, special processes, and/or laser trimming can be used to reduce matching errors, these methods lead to significant cost increases. The DEM technique accepts matching errors as inevitable and dynamically rearranges the interconnections of the mismatched elements so that on the average the element values are nearly equal. If the mismatched components are rearranged properly, the errors caused by them can be reduced or eliminated.
Existing DEM structures are used in designing real-time circuits, including DEM analog-to-digital converters. However, DEM digital-to-analog-converters are plagued by time-local nonstationarity and require exceedingly long and random switching sequences to achieve adequate “average-performance” improvement. Thus, problems remain with the use of DEM structures.
What is needed is an improvement in the state of the art of testing. Therefore, it is a primary object, feature, or advantage of the present invention to improve upon the state of the art.
It is a further object, feature, or advantage of the present invention to provide a method of analog and/or mixed-signal circuit testing which can be used for either BIST or production environments.
A still further object, feature, or advantage of the present invention is to provide a method of analog and/or mixed-signal circuit testing that provides test signal generation that is fast.
A still further object, feature, or advantage of the present invention is to provide a method of analog and/or mixed-signal circuit testing that provides test signal generation that requires nominal design effort and nominal silicon area to implement.
A still further object, feature, or advantage of the present invention is to provide a method of analog and/or mixed-signal circuit testing that provides test signal generation that does not require calibration or testing.
Another object, feature, or advantage of the present invention is to provide a method of analog and/or mixed-signal circuit testing that is of reasonable cost.
Yet another object, feature, or advantage of the present invention is to use a DEM structure, not in the DUT, but in the signal generator thereby eliminating the real time concern when using DEM.
These and/or other objects, features, or advantages of the present invention become apparent from the specification that follows.